The invention relates to a device and a method for the automatic inspection of ophthalmic lenses, especially contact lenses, in an automatic lens manufacturing process.
The production of contact lenses using conventional methods, such as rotary processes for hard contact lenses and pouring processes for soft contact lenses in disposable plastic moulds is relatively expensive. As a rule, these contact lenses are used for a period of one year to one month. However, technical advancement in recent years has enabled contact lenses to be produced, which are worn only on one day and are replaced afterwards by new contact lenses. However, this has been made possible only through a high degree of automation of the production plants. Production of these contact lenses advantageously takes place using reusable mould halves, the matrix and the patrix, which normally consist of glass or quartz. Between these mould halves is a hollow cavity, which corresponds to the subsequent contact lens shape. Before closing the mould halves, a polymer solution is measured into the matrix. The upper mould half is exposed to UV light, which leads to crosslinking of the lens material. Subsequently, the lens is removed from the mould half with suction grips and is placed in the pack.
In order to assure constant quality of the contact lenses, provisions are in place for automatic inspection of the contact lenses using industrial image-processing methods. In image-processing, the lenses are tested both in the mould halves and at the vacuum grips. An image processing method of this kind is described for example in EP patent 491 663. Moreover, using optical methods, not all defects of contact lenses can be detected without problems, so that defective contact lenses pass the quality control as defect-free and it is only the customer who establishes the defects when he removes the lens from the pack or even when he first wears the contact lens.
The invention is based on the problem of providing an inspection device and an inspection method, which recognise the defective lenses, which are difficult to detect with conventional optical methods, with a high degree of reliability.
According to the invention, the contact lenses are exposed to an ultrasonic field, which leads to destruction of defective lenses, while perfect lenses are as a rule not destroyed. In particular, the method is capable of detecting cracks in contact lenses which are often overlooked by optical methods, since this type of defect reacts especially sensitively to the soundwaves being received.
Further details and advantages of the invention may be seen from the description that follows and the drawing. In the drawing,